Top Republicans urged Akin to withdraw from the race after he suggested women who are victims of "legitimate rape" are unlikely to become pregnant. He refused, and support and money have begun returning to his campaign.
Akin said McCaskill's aggressive behavior in their first debate Friday convinced him she now thinks he is a formidable opponent, The Kansas City (Mo.) Star reported. He said she is "out of step badly" with Missouri voters while she tries to paint him as an extremist.
"I think we have a very clear path to victory, and apparently Claire McCaskill thinks we do, too, because she was very aggressive at the debate, which was quite different than it was when she ran against Jim Talent," Akin said. "She had a confidence and was much more ladylike (in 2006), but in the debate on Friday she came out swinging, and I think that's because she feels threatened."
The National Republican Senatorial Committee said Wednesday McCaskill must be defeated.
"There is no question that for Missourians who believe we need to stop the reckless Washington spending, rein in the role of government in people's lives, and finally focus on growing jobs in this country, that Todd Akin is a far more preferable candidate than liberal Sen. Claire McCaskill," National Republican Senatorial Committee Executive Director Rob Jesmer said in a statement.
Former GOP presidential hopeful Rick Santorum and Sen. Jim DeMint, R-S.C., a leading member in the Tea Party movement, said Wednesday they backed Akin, a day after the final deadline passed for him to get off the ballot.
"Todd Akin is a principled conservative who is committed to winning and fighting for freedom in the U.S. Senate," Santorum and DeMint said in a joint statement.
Sen. Roy Blunt, R-Mo. -- who had been charged with trying to get Akin to drop out of the race after he said rape victims had a natural ability to avoid pregnancy if the rape was "legitimate" -- also said he supported his fellow Missourian in his race for incumbent McCaskill's seat.
Establishment Republicans have said the race is lost, but Akin trails McCaskill only by single digits in polls. Some Republicans have suggested Akin might still have a chance to win the seat, The Washington Post reported.
Sen. Patty Murray, D-Wash., the head of the Democratic Senate campaign committee, called GOP support for Akin "absolutely shameful."
"All Republican candidates across the country are now going to have to answer for their party's support of Akin," she said in a statement.
Democratic Senatorial Campaign Committee spokesman Shripal Shah said, "No one should've been fooled by the Republican Party's faux outrage and their ensuing change of course, because as the Republican establishment is making clear today, the Akin backlash was never about principle; it was purely about politics."
The NRSC said after Akin's "legitimate rape" comment it would not spend money on his behalf this fall.
The committee declined to tell The Washington Post Wednesday if its switch to support Akin now meant it would spend money on his campaign. It said it didn't want to telegraph its strategy.
Major conservative "super PACs," including American Crossroads and Crossroads GPS, pulled out of Missouri and halted their multimillion-dollar ad campaigns against McCaskill.
Akin has apologized, saying he "misspoke," but has campaigned on the support he received from those who shared his view. He opposes abortion, even in the case of rape and incest.